Enchanted underwear only has a stated per day toxicity reduction between 2 and 4. I say "stated" because upon checking the code I found an error which completely negates the effect, my bad. Fortunately it's not a data corruption so once it's fixed it should work as stated. I'll try to add it to the bugfix mod soon.
There are no other items besides the potions and enchanted underwear(when fixed) that effect toxicity, without mods. I've checked every game file containing "tox". The Living Suit underwear only effects lust.
There are many potions that if even a single one is used alone can take an around 24 days for the toxicity to return to zero (40 toxicity can take 8-40 days).